Performance and Manufacturing of Silicon-Based Vapor Chambers

Enhancing heat transfer performance of aluminum-based vapor chamber with a novel bionic wick structure fabricated using additive manufacturing

Experimental analysis of thin vapor chamber with composite wick structure under different cooling conditions

Thermal management of electronic components is critical for their efficient, safe, and reliable operation. In this regard, vapor chambers are widely used to dissipate very high flux and avoid failures due to sudden temperature rise. Thermal performance of these devices is significantly dependent on component/evaporator mounting. When evaporator is mounted on the top (i.e., adverse gravity condition), essentially wicks are required in between evaporator and condenser of the vapor chamber to return the condensed liquid to the evaporator. However, wickless vapor chambers fail in such conditions, where gravity does not assist vapor removal and also does not allow condensed liquid to return evaporator end. Recently, we demonstrated a completely passive strategy of vapor removal even in adverse gravity condition using the surface-active additives (ionic liquids and surfactants) during pool boiling. In this work, we investigate the thermal performance of a confined wickless chamber using the aqueous surface-active additive solution as the test fluid. Design of the chamber is such that no wicks are required. The working mechanism of the present wickless chamber allows it to perform even in adverse gravity condition. We believe this strategy will prove to be a reliable solution for effective thermal management of earth electronics for mounting independent operations.

Numerical simulation of a heat sink embedded with a vapor chamber and calculation of effective thermal conductivity of a vapor chamber

Performance and two-phase flow pattern for micro flat heat pipes

The worldwide power electronics market is expected to expand at an annual growth rate of 4.7% from USD 35.1 billion in 2020 to USD 44.2 billion by 2025 [1]. This rise is fueled by the use of renewable energy sources throughout the world, and the increasing utilization of power electronics in the production of electric vehicles. The expanding implementation of power electronics in consumer products is another key driver of the market's growth. The most significant impediment in the electronic systems is their thermal management. Two-phase cooling is currently the standard thermal-management solution in all its forms, including heat pipes, vapor chambers, thermosyphons, and so on. But comparing the performance of different systems poses many challenges, thus making decision making difficult in the absence of complete information for each device.In this study, a list of ten critical elements or parameters required to unambiguously characterize the design and performance of a promising two-phase heat-transfer system for future deployment and development, namely the vapor chamber, is presented. This "Decalogue" is inspired by three main factors. First, the rising demand for better and more effective vapor chamber assemblies, which has prompted both industry and academia to invest substantially in related R&D. Second, this investment has resulted in a plethora of new systems (i.e. [2] –[6] etc.) where each design has been accompanied with insufficient description, making it difficult, if not impossible, to perform detailed comparisons across different designs/approaches. Third, the need to develop a common set of standards for describing such systems so that similar designs/philosophies may be compared successfully by researchers and developers seeking to duplicate results and improve on previous performance, especially in commercialized systems.We seek to gather all criteria needed to characterize each vapor chamber system, while exhibiting all benefits and limitations of its design, and illustrating what type of technical application the design may be helpful for, using a simple tabular method. The suggested approach might serve as a reference point or a standard way of accurately representing this type of heat transfer component. This description should benefit researchers in the area by clearly stating what the actual measurements/attributes of each system are, while also emphasizing the relevance/importance of each design by simply comparing it to others. The ten (deca) points presented here merely illustrate the most essential aspects of the design and performance of any vapor chamber.

A cascaded multicore vapor chamber (CMVC) is designed for dissipating heat from high-flux hotspots simultaneously with a high-total-power background. Current thermal management strategies rely on spreading high local heat fluxes by conduction in the lid of electronics packages. Embedding vapor chambers (VCs) within the lid is an attractive option to directly address intrapackage hotspots. We investigate the design of intralid VCs, for a generic device having a total heat load of 476 W having a background heat flux of 0.75 W/mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , with hotspots of 8 W/mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> over a 1-mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> area. A conventional VC design, having a single vapor core, will require a thick evaporator wick to avoid the capillary limit for large total power. The necessity for a thick wick then imposes a large thermal conduction resistance when the VC is exposed to high heat flux hotspots. The proposed CMVC architecture aims to address this limitation. The cascaded architecture comprises a bottom-tier VC having an array of multiple small vapor cores for spreading heat from the small hotspots. These small vapor cores have short paths of liquid return to the evaporator, such that they can handle their footprint heat load while using thin wicks, resulting in a low hotspot thermal resistance. Furthermore, local dampening of the hotspots by the bottom tier then reduces the thermal conduction resistance across the necessarily thick wick in the top tier. Hence, the cascaded architecture has the potential to significantly reduce the overall thermal resistance, relative to a single tier. To substantiate this design rationale, experiments are performed to illustrate that the resistance of a commercial VC can be significantly reduced by interfacing the heat source with an intermediate heat spreader. Reduced-order models are then used to understand the effect of the wick properties (porosity and particle size) and geometric parameters on the thermal performance of the CMVC for the representative power map. The optimal CMVC design offers a thermal resistance (0.66 K/W) that is significantly lower compared to a conventional single-core VC (1.76 K/W) owing to a reduction in the conduction resistances across the internal wicks. That parametric optimization results demonstrate that the thermal resistance of the CMVC is more sensitive to the wick porosity compared to the particle diameter. Furthermore, there exists a wide range of wick properties and vapor core sizes for which near-optimum thermal performance can be attained, which is particularly attractive from the standpoint of flexibility in design and manufacturing.

Performance tests on a novel vapor chamber

An Investigation into the Effective Thermal Conductivity of Vapour Chamber Heat Spreaders

With the rapid spread of high-power density equipment, the vapor chamber must adapt to more applicable environments and exhibit a better heat transfer performance. The copper mesh and powder are sintered in this work to make a composite wick vapor chamber (CW-VC). Six sections of copper wire are cut and sintered together with the wick as the inner support column of the CW-VC. The effects of filling ratio and inclination on the heat transfer performance of the vapor chamber are investigated. The experimental results showed that the maximum thermal power of the CW-VC is 23.29 W at the optimal liquid filling ratio of 80% and the lowest thermal resistance is 0.33 °C/W. Below the liquid filling ratio of 60%, when the inclination angle of the CW-VC increases, its thermal resistance increases. At filling ratios of 70%, 80%, and 90%, the inclination angle of 30° can reduce the thermal resistance of the CW-VC. It implies that the inclination angle of the CW-VC can be increased appropriately to reduce the thermal resistance when the filling ratio is high. However, when the liquid filling ratio is low, increasing the inclination angle of the CW-VC will make the liquid film of the evaporator thinner and dry out earlier and its thermal resistance will increase.

Sensitivity and optimization analysis of pillar arrangement on the thermal–hydraulic performance of vapor chamber

Significant factors affecting heat transfer performance of vapor chamber and strategies to promote it: A critical review

This paper introduces a simplified modeling scheme for the prediction of heat transport capability of heat pipes and vapor chambers. The modeling scheme introduced in this paper enables thermal designers to model heat pipes and vapor chambers in commercially available conduction modeling tools such as Ansys™ and IcePak™. This modeling scheme allows thermal designers to perform design sensitivity studies in terms of power dissipation of heat pipes and vapor chambers for different scenarios such as configurations, heat sink resistance for a given temperature drop between the heating source and the ambient. This paper also discusses how thermal designers can specify requirements to heat pipe/vapor chamber suppliers for their thermal design, without delving into the complete thermo-fluidic modeling of this technology.

In this paper, a large size aluminous vapor chamber (650 mm × 350 mm × 5 mm) with high effective thermal conductance and light weight was developed for heat dissipation of high heat flux point heat source in aircrafts near space. The heat performance of aluminous vapor chamber (VC) was tested in a power range of 50 W to 159 W. The heat resistance is about 0.2 ℃/W under a heat flux of 25 W/cm2, and the chamber works normally without dryout under a power condition as high as 159 W (~43 W/cm2), which indicates its capability under high heat flux. To enhance thermal performance of aluminous vapor chamber, an integration heat spreader which integrated of advanced carbon materials (annealed pyrolytic graphite, multilayer graphene) and aluminous vapor chamber was fabricated. The test result shows integration heat spreader can significantly reduce the heat spreader resistance of aluminous vapor chamber: the temperature difference between the evaporator section and condenser section decreases from 39.6 ℃ to 9 ℃ under a heat rate of 130 W (heat flux 36.5 W/cm2), while the heat resistance reduces from 0.3 ℃/W to 0.07 ℃/W. Also, the effect of gravity has been studied under horizontal placement and vertical placement. The result shows the thermal resistance under vertical placement is about 3–4 times of that under horizontal placement.

A fin heat sink (FHS) is a thermal heat transfer device employed to dissipate heat from a high temperature heat source to a lower temperature surrounding. A typical FHS consists of a flat metal base with an array of cooling fins on top. A problem normally encountered in thermal management of electronic packages is thermal heat spreading resistance which occurs as heat flows by conduction from a high temperature heat source to a low temperature heat sink with different cross-sectional areas. As high powered semiconductor chips are made more compact and requiring greater heat dissipation, more effective cooling systems have to be devised. There are various methods employed to minimize this heat spreading resistance. These include increasing the thickness of the base of the FHS or height of the fins. Another method is to use more expensive highly conductive materials like aluminum, copper and diamond which would increase cost. A more economical alternative would be to combine a flat heat pipe (HP) sometimes termed a vapor chamber (VC) with a conventional FHS to increase effective thermal conductivity at the base. Thermoelectric (TE) is the direct conversion of temperature difference between the junctions of two dissimilar materials (thermocouple) to electricity. The converse is true. A voltage applied between the junctions of the thermocouple creates a temperature difference between them. This effect could be utilized as a heat pump to transfer heat from the cold junction to the hot junction. A dc voltage imposed across a thermoelectric (TE) module causes a temperature difference to be imposed across the surfaces of the resulting in one face to be at a temperature higher than the other face. Heat is absorbed from a heat source in contact with the cold surface and dissipated to a heat sink in contact with the hot surface. This paper presents the results of an investigation conducted to evaluate the performance of VCs and TEs for the thermal management of LEDs.